Looking Up: Sirius, a diamond’ in the sky

Friday

Feb 11, 2011 at 12:01 AMFeb 11, 2011 at 11:13 AM

Someone somewhere in an advertising department, most likely, came up with “Diamonds are a girls’ best friend.” What with Valentine’s Day approaching fast, a timely topic this week is not just a sparkling reminder of a beautifully cut diamond, but “man's best friend” as well.

Peter Becker

Someone somewhere in an advertising department, most likely, came up with “Diamonds are a girls’ best friend.” What with Valentine’s Day approaching fast, a timely topic this week is not just a sparkling reminder of a beautifully cut diamond, but “man's best friend” as well.

You see, while the lady prefers diamonds, it appears the gentleman is content with a dog. How about both, the next clear night- the constellation Canis Major the Big Dog with a brilliant star named Sirius shining like a diamond for his collar?

Often called the “Dog Star,” Sirius is the brightest star visible in the sky after our own sun. Sirius rules the night, outshone by only the Moon, planets Venus and Jupiter, and the rare brilliant meteor. The star is likened to a diamond in appearance due to its bluish-white hue and sheer magnitude. Winter evenings are an excellent time to see it. The star gleams about a third of the way up in the southern sky (as seen from mid-northern latitudes), on February evenings.

You will see to the lower left of the bright constellation Orion, but Sirius really needs no pointers. There are no stars at night its equal.

Its magnitude is minus (-) 1.46. Although it puts out 23 times the light as does our sun, Sirius appears as bright as it does mainly because it is so near. The star is the fifth closest star system, a mere 8.7 light years away. That’s still over 50 TRILLION miles away, but just down the block by galactic standards. The light you see tonight from Sirius left on its journey to your eyes 8.7 years ago.

It is so bright, that under excellent sky conditions, Sirius has been seen in broad daylight. The hardest part is knowing exactly were to look. This is best done in the southern hemisphere, where Sirius is seen very high up.

The impression of a radiant diamond is most keen when you see Sirius in any size telescope. The bigger the telescope, the brighter it will be, and it is an amazing sight. Even binoculars give an outstanding view of Sirius’ light.

The ancient Egyptians revered Sirius as signaling the beginning of the annual flooding of the Nile, when the star was first seen in the early morning before dawn.

Orbiting the star once every 50 years is a much dimmer star, called Sirius B, or better yet, “The Pup.” Shining at magnitude +8, this star would be easily seen in binoculars but is lost in the glare of Sirius. It is a challenge even to see it in a typical backyard telescope, due to the overpowering Dog Star.

The Pup varies in its distance from Sirius from about as near as planet Saturn is from the sun to as far as Neptune.

This companion star was discovered in 1862 by an American astronomer and famed telescope maker, Alvan G. Clark. The star was suspected since 1844 when slight shifts were observed in Sirius’ motion against the sky - a previously unknown companion was tugging on the brighter star.

Physically, Sirius is almost twice the diameter of our Sun with 2.35 times as much material (mass). Its faint companion star is heavy indeed. The Pup is 40 to 50 times SMALLER in diameter than the sun but has a mass about equal to our star. Classified as a white dwarf star, the Pup is so dense, a cubic inch of its material would weigh about 2.25 tons. The sun’s density is only about a half ounce per cubic inch!

While Sirius has the “Pup,” another “puppy” is close by-the small constellation Canis Minor the Little Dog, is to the upper left. Canis Minor has only two stars well seen by unaided eyes. One is quite bright, 0-magnitude and yellow and named Procyon.

Men, if you are a bit short in the wallet this Valentine’s Day, you can take our sweetheart out to enjoy the diamond of the sky, Sirius, free of charge. Ladies, you can show him the Big Dog!